Recently, a method has been adopted for medical treatment and diagnoses which is carried out through a lumen formed inside a catheter after the catheter is inserted into a biological lumen such as a blood vessel so as to reach a target site. Generally, a catheter includes a long tubular catheter body and a catheter hub which is interlocked with a proximal portion of a catheter body. Catheter bodies have been decreased in thickness so as to maximize the inner diameter in order to secure a wide space in a lumen. Catheter development has progressed to the point that catheters can be inserted into a blood vessel narrower than the femoral artery such as the radial artery. A decreased outer diameter necessary for a catheter body to be inserted into a narrow blood vessel also promotes reduction in thickness of the catheter body.
A decreased thickness of a catheter body may result in collapse and kinking (bending) of the catheter body due to degraded strength thereof, and thus, it may be difficult for the catheter body to pass through a bent blood vessel. Moreover, due to an occurrence of collapse and a kink, it is difficult for a medical instrument or liquid such as medicine and a contrast agent to pass through the inside of a lumen. As the strength of a catheter body is degraded, it is difficult for the catheter body to be thrust forward in a blood vessel due to a degraded pushing performance (pushability) thereof. In addition, the decreased thickness of a catheter body causes a distal portion of the catheter body to be sharp, and thus, biological tissue is easily damaged.
In order to decrease an occurrence of collapse and a kink while decreasing the thickness of a catheter body, a method has been proposed in which a catheter (an inner catheter) or a dilator is inserted into another catheter (an outer catheter) (for example, refer to Japanese Application Publication No. 2004-357805). As a shaft such as an inner catheter is inserted into an outer catheter, appropriate stiffness can be applied by the shaft while decreasing the thickness of the outer catheter. Thus, an occurrence of collapse and a kink can be suppressed when the catheter is inserted into a blood vessel, and a pushing performance can also be improved.